From waste to building material: How whey ultrafiltration permeate can increase wood stability

Wood has a lower carbon footprint compared to many other materials used in construction. However, its hygroscopic nature poses significant challenges, including dimensional fluctuations in response to humidity shifts. Here we investigate a new treatment method mitigating swelling and shrinkage using dairy by-product named whey ultrafiltration permeate (mainly composed of lactose) and citric acid. Trembling aspen and black spruce samples were impregnated with ultrafiltration permeate and citric acid. Infrared and Raman spectroscopy were used to evaluate the esterification reaction and the location of the impregnates. We found increased ester bonds in the cell walls and the middle lamella (leaving the lumens empty), explaining the improved wood stability. Trembling aspen was more receptive to the treatment than black spruce, as shown by a higher weight gain (39 % vs. 13 %) and anti-swelling efficiency (54 % vs. 37 %). No leaching was observed during characterization of the treated wood. The modulus of elasticity and rupture, and the Brinell hardness were only slightly affected for both wood species. Upon combustion, esterified wood samples degraded at a lower temperature, but the stability of the residues was increased. This study highlights a promising use of ultrafiltration permeate in wood esterification.